Understanding Block Scope with let in JavaScript – Asked in a Mindtree Interview

Our Javascript Code :-

let x = 10;
{
    let x = 20;
}
console.log(x);

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Step-by-Step Execution

🔸 Step 1: Declare x in the global (or outer) scope

let x = 10;

• A variable x is created in the outer/global scope, and its value is 10.

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🔸 Step 2: Enter a new block

{
    let x = 20;
}

• This {} is a block.
• Inside this block, you declare a new variable also named x using let.
• ⚠️ This does not override the outer x! It's a completely separate variable scoped only inside the block.

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🔸 Step 3: Exit the block

Now you're outside the block, so the x from inside is gone — it was block-scoped.

The only x still alive is:

let x = 10;

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🔸 Step 4: console.log(x)

You are now in the outer scope, so you're accessing the outer x.

Therefore:

console.log(x); // 10

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✔ Final Answer:

B) 10

This question appeared in the Mindtree 2nd round of interview, testing the candidate’s knowledge of functional scope and block scope when we declare a variable using let keyword in JavaScript.

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➡ Some points about "let" keyword

• Introduced in ES6
• Block-scoped (unlike var, which is function-scoped)
• Cannot be redeclared in the same scope
• Useful for avoiding unintended overwrites